1. Field of the Invention
The invention relates to a double row ball bearing, and more particularly, to a so-called tandem double row ball bearing that is lubricated using lubricant housed in a final reduction gear of a vehicle and is suitable to support a pinion shaft.
2. Related Art
A tandem double row ball bearing includes an outer ring, an inner ring, and balls disposed in double rows between both of the rings, and a cage for retaining the balls. The double row ball bearing has been widely used in a pinion shaft supporting device for vehicles or the like as shown in JP 2006-234100A.
FIG. 2 illustrates an example of a differential gear device to which a double row ball bearing according to the invention is applied. The differential gear device includes a pinion shaft 42 that is rotatably supported to a housing 41 and has a pinion gear 43 disposed at a rear end thereof; a ring gear 44 engaging with the pinion gear 43; a pair of double row ball bearings 45 and 46 that allows the pinion shaft 42 to be rotatably supported to the housing 41, the double row ball bearing 45 being located on a side of the pinion gear 43 and the double row ball bearing 46 being located on as side opposite to the pinion gear 43; and a flange joint 47 is provided at an outer end of the pinion shaft 42 to connect a drive shaft.
In the differential gear device, lubricant flipping up according to rotation of the ring gear 44 is introduced at a middle portion along the axial direction between the pair of double row ball bearings 45 and 46 through a lubricant passage 48 provided in the housing 41. When the double row ball bearings 45 and 46 are rotated, a fluid flow (pumping action) occurs from a small diameter side to a large diameter side. Accordingly, in the double row ball bearings 45 and 46 for differential gear device, the small diameter side of each of the double row ball bearings 45 and 46 is located close to the shaft, and the lubricant is supplied from the small diameter side (accurately middle portion between one pair of double row ball bearings) and is discharged from the large diameter side by the pumping action. Such a lubricating method has been generally applied.
In such a kind of double row ball bearing, a large diameter cage for retaining a plurality of large diameter balls and a small diameter cage for retaining a plurality of small diameter balls are used as cages. These cages have a similar shape except for difference in diameter. That is, in the general double row ball bearing, the large diameter cage and the small diameter cage are formed substantially in a conical asymmetrical shape. On the contrary, in JP 2006-234100A, the large diameter cage and the small diameter cage are formed substantially in a cylindrical symmetrical shape.
In the pinion shaft supporting devices for vehicles, in order to reduce loss, it is important to reduce rotational torque of a bearing. In order to reduce the rotational torque, it is effective to suppress agitation resistance caused by lubricant. According to the double row ball bearing described in JP 2006-234100A, the small diameter cage has a symmetric shape to suppress the amount of flowing-in lubricant, thereby suppressing agitation resistance caused by lubricant. However, in JP 2006-234100A, since the large diameter cage has a shape similar to that of the small diameter cage except for difference in diameter, the amount of flowing-out lubricant is suppressed. Accordingly, the amount of lubricant staying in the bearing increases and thus the effect to reduce agitation resistance may decrease.